Alarm system



Filed Feb. 18, 1937 FIG/ . INVENmR LA. GARDNER 7 WJW A 7' TOP/VEVPatented Mar. 12, 1940 UNITED STATES ALARM SYSTEM Leland A. Gardner,Maplewood, N. J., assignor to Bell Telephone Laboratories, Incorporated,New York, N. Y., a corporation of New York Application February 18,1937, Serial No. 126,414

9 Claims.

This invention relates to alarm systems and particularly'to hitindicators for electrical circuits such as telegraph systems.

Line hits are defined as short open pulses or other forms of lineinterference which impair transmission over the line. Since these hitsproduce errors in the messages received, they must be detected and thefault must be eliminated as promptly as possible. A number of alarmsys-.

10 terms for this purpose have been proposed heretofore and when suchsystems are used at repeater stations of a telegraph system, they areefiective to indicate line trouble when the line is idle or when signalsare being transmitted from the repeater to the line under test. However,when the direction of transmission reverses the alarm is operated evenwhen there is no line trouble as the system is incapable ofdiscriminating between line interference and signals being received fromthe line.

The object of this invention is an efiicient and reliable hit indicatorcircuit by means of which an attendant may distinguish readily betweenline interference and a reversal in the direction of transmission overthe line being tested.

According to the invention, as applied to a tele I graph system, agas-filled trigger tube is asso-' ciated with the line in such a way asto be flashed upon the occurrence of a line hit or an incoming signalpulse thereby completing a circuit including a recording device or anindicating device such as a lamp. In one embodiment of the invention akey is provided for resetting the tube, extinguishing the lamp andpreparing an alter- 5 nate control circuit for the lamp of such a natureas to produce a flashing of the lamp at 'a predetermined frequency ifsignals are being received from the line. When the lamp is lighted theattendant operates the key and if the lamp flashes 40 he does not regardthe first operation as an indication of trouble unless the signal isrepeated after the incoming signals cease.

In another embodiment of the invention the first flash of the gas-filledtube lights the hit 45. lamp and automatically prepares a controlcircuit for a second lamp which flashes as long as signals are beingreceived. When transmission ceases, the attendant resets the tube anddisregards the first hit indication unless the hit lamp only isrelighted.

The invention and the manner in which it may be utilized in systems ofvarious types will be more clearly understood from the following detaildescription and the accompanying drawing in which Fig. 1 shows. an alarmsystem or hit indicator according to the invention which has only asingle indicating device and which is adapted for use with telegraphrepeaters wired for test board answering; 1 i 5 Fig. 2 shows a similarsystem adaptedto be connected as a loop leak or armature leak circuit:

Fig. 3 shOWS an alternate alarm system having separate hit andtransmission indicators and adapted for use with test board answeringrepeaters; and

Fig. 4 shows the lternate system of Fig. 3 adapted foruseas a loop leakor armature leak circuit.

In Fig. 1' the hit indicator circuit is shown associated with atelegraph repeater and the line L. The repeater comprises the usualreceiving relay R, the armature of which cooperates with the markingcontact 111. and the spacing contact 5, and the sending relay S togetherwith the other apparatus (not shown) which is usually associatedtherewith. The repeater shown is also provided with a jack H and a cordl2 whereby the repeater circuit is extended to a jack l3 at the testboard where the hit indicator circuit is located so as to be readilyavailable for use on any one of a number of such repeater circuits.

The indicator comprises a gas-filled tube I4 having in its outputcircuit a relay I5 for controlling the lamp E6 or other indicating orrecording 30 device. When the line is idle or when signals are beingsent out from this station, the armature of the relay R is normally'atrest on its marking contact m as shown. The potential dropin theresistor 9 maintains a steady current in the primary of the transformer89 and the grid ll of the tube is negatively biased by the battery l8 sothat under this condition the tube is blocked and no current flows inthe plate circuit.

The transformer Ii! is connected to the repeater with the properpolarity so that for changes in the line current which would tend .tomake the armature of the relay R leave its marking contact m, thepotential induced in the transformer secondary reduces the bias onthegrid l1 and permits a current to flow in the plate circuit of the tube.This current operates the relay 15 which lights the lamp l6 andcompletes a holding circuit for the relay extending from the groundedbattery 20 through the key 2! conductor 22, the holding winding on therelay conductor 23, key 2 l, the contacts of the relay to ground at thelamp it. While the change in potential across the resistor 9 when a hitoccurs on the linewill ordinarily be only a few volts the trans- 55relay at jack 33.

the winding and contact 45 of former I9 is preferably selected so thatthe voltage induced in the secondary is relatively large. Under thiscondition the system is very sensitive and may be adjusted to detecteven line disturbances which are not of sufiicient magnitude to producea false operation of the receiving relay.

The attendant observing that the lamp is lighted operates and holds thekey 2|. The breaking of the normally closed contacts 24 and 25 breaksholding circuit of the relay and the plate circuit of the tube therebyreleasing the relay, resetting the tube, and extinguishing the lamp. Themaking of contacts 26 and 21 prepares the plate circuit through the twowindings and contact 28 of the relay but if the lamp was lighted by aline hit the relay does not reoperate since the tube has been reset. If,however, the direction of transmission has reversed and signals arecoming in, the next space impulse again flashes the tube, operates therelay and opens contact 28 so that the plate current is diverted throughthe resistor 29 and the condenser 30 and is gradually reduced to zero asthe condenser is charged. This delays the resetting or deionization ofthe tube and the release of the relay but when the current reaches somelower value the relay releases, extinguishing the lamp and closingcontact 28 to discharge the condenser through the resistor 29. After thetube has reset the next space impulse repeats this cycle and the lamp I6 flashes at a frequency determined by the values of the resistor 29 andthe condenser 30. Due to the thermal lag of the filament, the lampcannot flash at the frequency of the line signals and in the absence ofthe condenser and resistance would remain either lighted or out, butwith a suitable circuit of the type shown it may be made to flash at alower frequency to produce a characteristic indication of reversedtransmission.

The hit indicator portion of the circuit of Fig. 2 is quite similar tothat of Fig. 1 except that the transformer I9 is replaced by a couplingresistor 3!, which is connected to the repeater by means of a singleconductor cord 32. This type of hit indicator input circuit isparticularly applicable for connection to points in the system where thechange in voltage when a hit occurs is large enough to flash the tubewithout the use of a transformer. This is true, for example, when theindicator is used in a subscribers loop by plugging the cord 32 into thejack ill or when it is connected to the armature of the receiving Ineither case when a hit occurs the normal bias on the grid ll of the tubewill be reduced, the tube will flash and the indicator will function inthe same manner as already described in connection with Fig. 1.

The indicator of Fig. 3 has an input circuit of the type shown in Fig. land the indicator of Fig. 4 has an input circuit of the type shown inFig. 2. In the circuits of both Figs. 3 and 4, a hit or an initial spaceimpulse flashes the tube l4 and operates the relay l5 over a circuitextending from the battery 26 to key 47, the operating winding of therelay, relay contact 4! to the plate of the tube. The operation of therelay closes contact 42 to lock in the relay and the hit lamp 43 andopens contact 4! to reset the tube and closes contact 44 therebytransferring the plate circuit of the tube to the battery 20 through therelay 46. If the foregoing operations were caused by a line hit, nothingfurther occurs, the attendant records the hit and momentarily opens thekey 4'! to release the relay l5 and extinguish the lamp. If,

' ly operating. said indicating means means for conditioning the tube toreset however, the lamp 43 was lighted by a reversal of transmission,the relay 46 will be operated by succeeding space impulses and willflash the transmitting lamp 48 at a predetermined irequency determinedby the valves of the resistor 49 and the condenser 50 as in the circuitof Fig. 1. It will be observed that the hit indicator of Figs. 3 and 4distinguishes between line hits and transmission without any action onthe part of the attendant. This is a material advantage in that theattendant, when busy on some other work at a distance from theindicator, may ignore the hit lamp 43 as long as the lamp #8 isflashing. When transmission from the line ceases, he momentarily opensthe key 41 to extinguish the lamp 43 and condition the indicator torespond to any subsequent hits.

While the invention has been disclosed with reference to its applicationto a telegraph repeater, it will be understood that it may be used anindicating device, of a relay controlling the device and having normallyclosed contacts, an output-circuit for the tube extending through theWinding and the closed contacts of the relay,

and means comprising a condenser shunting said contacts efiective uponthe opening of the con tacts to delay the resetting of the tube.

2..In a hit indicator for telegraph circuits, the combination with anormally blocked, gas-filled tube adapted to be flashed by-an impulsefrom a telegraph circuit and indicating in a first manner by theflashing of the tube in response to a hit .or a reversal in thedirection of the transmission of signal pulses, of means forconditioning the tube to reset automatically after a predetermined delayand means for subsequentin a second manner, in response to a reversal inthe direction of transmission of said pulses.

3. The combination with a normally blocked gas-filled tube, means forflashing the tube and an indicating device operated by the tube, ofmeans for resetting the tube and the device, automatically ata firstrate, and means comprising a condenser temporarily eiiectively in seriesbetween the anode of said tube and positive battery operative when thetube is so conditioned for changing said rate of resetting of the tube.

4. The combination with a normally blocked gas-filled tube, means forflashing the tube, an

tween the anode of said tube and positive battery when said contacts areopen.

5. The combination with a normally blocked gas-filled tube, means forflashing the tube and two indicating devices, of a first relaycontrolling one of the devices and adapted to operate when the tube isflashed, a second relay controlling the other device and adapted tooperate when the tube is flashed while the first relay is operated, andmeans associated with'the second and output circuit for the tubecompleted by the operation of said one relay and extending through thewinding and closed contacts of the other relay.

7. A telegraph circuit, a hit indicator connected to said circuit, meanscomprising a normally blocked gas-filled tube and an indicating devicein said indicator for indicating both a circuit disturbance and a changein the direction of the transmission of telegraph signals in saidcircuit, means'also in said indicator comprising a condenser effectivelyin series between the anode of said tube and positive battery fordiscriminating between said disturbance and said reversal.

8. In a telegraph circuit hit indicator, means for discriminatingbetween a circuit disturbance and a reversal in the direction oftelegraph signal transmission, said means comprising a gasfilled tubehaving two different anode circuits, one of which contains a condenserinserieswith the anode and positive battery, said condenser being switchedinto said anode circuit intermittently.

I 9. In a hit indicator, a normally blocked gasfilled tube, an outputcircuit for said tube extend ing through the winding of a relay, adevice controlled by said relay for indicating that said tube hasflashed due to either of two conditions, means for maintaining saiddevice in the indicating con- ,dition, means in said hitindicatorcomprising a condenser effectively in series between the anode of saidtube and positive battery for resetting said tube and said device so asto discriminate between the said two conditions.

LELAND, A. GARDNER.

